Weird Hardware Serial Problem on Teensy 3.0

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PaulStoffregen said:
Oh, that doesn't sound right...




Do you believe it's a fundamental design problem with this Sparkfun product (eg, all of them would do this), or just one product that's damaged or defective?
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Hi Paul, we have 3 of them and only 1 have this strange behavior. I'd rather believe it is damaged by ESD or cosmic ray =P.

Regards,
Bai Shi
 
If the TX-O output is low when then the voltge on A is > B then that suggests a faulty chip/breakout board.

It's also possible that you have a case of a cold solder joint on the breakout. Since the RS485 signal is differential, it might work some of the time if the B input is left unconnected (floating CMOS inputs tend to capacitively couple to nearby signals).
 
baishi said:
Hi Steve,

Do you know how to invert the data? The UART you mentioned as in the UART in Teensy3 or the RS485 breakout? I couldn't dig it out though.

Actually my finding seems that the space and mark are identical to a brand new RS485 breakout. Just that the idle is different. It might not be inverting, just being pulled down on idle. I might be wrong though.

If you can advice how to set the inverting config, I can give it a try.

Best Regards,
Bai Shi
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This is probably not related to the RS484 issues, but as I recall, the UARTs in the K20 products have a configuration bit to invert the polarity of the transmitted data and expected received data polarity. I suppose this is to accommodate RS232/485 drivers that need or don't need polarity inversion.
 
baishi said:
we have 3 of them and only 1 have this strange behavior. I'd rather believe it is damaged by ESD or cosmic ray =P.
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Do you believe it might have been bad right out of the package, either a manufacturing defect or damage in shipping? Or was it more likely damaged while experimenting?
 
PaulStoffregen said:
Do you believe it might have been bad right out of the package, either a manufacturing defect or damage in shipping? Or was it more likely damaged while experimenting?
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Most properly damaged either during manufacturing or shipping. We didn't do anything funny with it, from the first usage it's giving this problem. I'd rather believe it was stroke by ESD or a cold solder joint. Either it is a little beyond my knowledge, I even don't know how to verify =(

Regards,
Bai Shi
 
PaulStoffregen said:
Please email me directly, paul@pjrc.com, and we'll arrange to get you a replacement. Be sure to put a link to this forum thread in your email.
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Er... Paul I think there is mis-communication here? I mentioned i have 3 of the sparkfun rs485 breakout and only one is broken. All Teensy work fine with the other two. If I understand correctly Sparkfun RS485 breakout is not PJRC product right?

Best Regards,
Bai Shi
 
Oh, yup, I misunderstood. I thought you were talking about the Teensy.

My guess is Sparkfun will probably replace that RS485 breakout board if you contact them.
 
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